Rechargeable lithium ion batteries help to enable sustainable energy systems by storing electricity generated by intermittent renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. However, the performance of lithium ion batteries degrades over repeated recharging cycles because of unwanted reactions that occur at the boundary between the battery electrode and the electrolyte. This project will develop new electrode materials for preventing these unwanted reactions. The key innovation is to coat nanoscale crystals of the lithium-based energy storage material with a very thin layer of other materials that are tailored to block these undesired reactions but maintain performance. The coating is uniformly applied to all the nanocrystals, and so that when the crystals are formed into an electrode, there are no gaps in the coating. The educational activities associated with this project involve mentoring of undergraduate students for summer research, and outreach to high school students in the Chicago area. The goals of the outreach activities are to communicate the value of energy storage technology in modern society to diverse groups of high school students in the Chicago area, and to encourage these students to pursue education and careers in STEM fields.
This overall goal of this research is to improve the ability of lithium ion battery cathodes to withstand extreme cycling environments by maximizing interfacial stability without sacrificing energy storage capacity, power delivery, and recharging time. Cathode-electrolyte instabilities have been linked to the presence of electroactive transition metals at the surface of the electrode. These instabilities result in irreversible transformations at these interfaces, with formation of insulating layers that impede transport as well as material loss due to corrosion. Core-shell architectures can address interfacial instability. The shell will be rich in inactive aluminum ions that minimize irreversible transformations at the interface, and the core will be composed of active transition metal oxides (Mn, Ni, Co) with high charge storage capacity. Furthermore, the shell will be thin to reduce storage capacity loss, and conformal to passivate all interfaces. To gain a fundamental understanding of the ability these core-shell cathode materials to maintain electrode stability, the research plan has three objectives. The first objective is to fabricate core-epitaxial shell nanocrystals for high voltage, high energy battery cathodes. The second objective is to design and evaluate core-shell architectures at the secondary particle level, and the third objective is to construct of full lithium ion cells and characterize of their interfacial mechanisms of operation. As part of this research, synthesis and fabrication tools will be developed to effectively coat all interfaces with tailored materials and create integrated cathode architectures where appropriate levels of electron and ion transport are imparted.
